Description of Related Art
Japanese Patent Publication No. 7-320842 discloses a connecting method of two different covered wires as shown in FIGS. 1A and 1B. The shown method is related to a connection between a shield wire W1 and a ground wire W2. The shield wire W1 has a core line 14 as a conductive part covered with a resinous cover 8 and a shielding braided wire 13 as another conductive part which covers the resinous cover 8 and is also covered with another resinous cover 7. While, the ground wire W2 has a core line 15 as a conductive part covered with a resinous cover 9.
In order to connect the shield wire W1 with the ground wire W2, it is executed at the first step to put the connecting (overlapping) part defined by the wire W1 and the wire W2 between a pair of resinous tips 1, 3. In detail, the resinous tip 3 is inserted into an anvil 5 and subsequently, the shield wire W1 is inserted into the anvil 5 and put on the resinous tip 3. Further, the ground wire W2 is inserted and put on the inserted shield wire W1 and finally, the other resinous tip 1 is laid on the ground wire W2.
At the second step, it is carried out to partially remove the resinous covers 7, 9 of the wires W1, W2 by heating the connecting part defined by the wires W1, W2 under pressure and further seal the resulting connecting part by welding the resinous tips 1, 3 each other. In detail, a horn 11 is inserted from the upside of the resinous tip 1 and continuously, the tips 1, 3 are heated due to ultrasonic oscillations between the horn 11 and the anvil 5 under pressure. Owing to the generation of heat by the ultrasonic oscillations, the covers 7, 9 are molten at the connecting part, so that the braided wire 13 of the shield wire W1 and the core line 15 of the ground wire W2 are exposed together.
While, the so-molten covers 7, 9 are pushed out of the resinous tips 1, 3 through a clearance therebetween, so that the braided wire 13 comes into electrical contact with the core line 15. With further continuation to both oscillate and pressurize, the resinous tips 1, 3 are molten for their integration, so that the connecting part can be sealed as shown in FIG. 1B.
In the above-mentioned connecting method, however, there is a possibility that the shield wire's portion close to the resinous tips 1, 3, i.e., a part 17, is influenced by the heat of the resinous covers 7, 9 pushed out of the resin tips 1, 3 (see FIG. 1B), thereby causing the deterioration of insulation effect, the disconnection of conductive wire, the deterioration of bending, etc.
FIG. 2 shows respective sections of the shield wire W1 and the ground wire W2 in their sealed connection which is somewhat different from the previously-mentioned connecting structure. Shown in the figure is a condition where a resin 19 resulting from the melting of the ground wire W2 is pushed out from the clearance between the resinous tips 1, 3, so that the ground wire W2 is damaged at its part 21 close to the tips 1, 3 by the heat of the so-pushed resin 19, causing the exposure of the core line 15.
Therefore, also in this case, there may be caused problems of the deterioration of insulation effect of the cover 9 at a part of the ground wire W2, the disconnection of the core line 15 and the deterioration of bending, too.